1. Field of the Invention
The invention relates generally to the field of magnetic motion converters. More particularly, this invention relates to uses for a device that converts rotary motion into axial motion by magnetic interactions, and applications of such devices in wellbore instruments.
2. Background Art
Wellbore drilling and servicing instrumentation includes percussion devices. Percussion devices include drilling “hammers” that convert flow of drilling fluid or rotational motion into reciprocating linear motion to cause a hammer bit or similar device to strike the bottom of the wellbore. The striking motion at least in part causes the wellbore to be lengthened. See, for example, U.S. Pat. No. 4,958,690 issued to Cyphelly. The device disclosed in the Cyphelly '690 patent converts flow of drilling fluid into reciprocating linear motion.
Typical reciprocating motion devices use eccentric rotation, e.g., camshafts, or use variations in hydraulic flow to reciprocate pistons which then provide the reciprocating output directly. Reciprocation may be generated without any solid surface coming into contact with another solid surface. One of the drawbacks inherent in reciprocating motion devices is that vibration from the device is conducted to other supporting elements associated with the device, e.g., portions of a drilling tool assembly (tool “string”). Such vibration can be damaging, particularly when there are sensitive electronic devices located near the reciprocating device, which is usually the case with tools such as directional drilling assemblies and logging while drilling (“LWD”) tools. Hammer drills such as the one disclosed in the Cyphelly '690 patent also typically have high fluid pressure losses associated with them, which can limit the wellbore depth in which they can be used when considering the total system fluid pressure losses.
Another device for generating reciprocating linear motion from rotary motion is described in International Patent Application Publication NO. WO 2006/065155 filed by Pfahlert.
There Continues to be a Need for Reciprocating Motion Devices that can be Used with Wellbore Instrumentation.